Posted: 14/08/2017 at 11:17
Pull or fork out the weeds you can get hold of then smooth down the soil. Using a large garden fork, go over the entire space pushing it in as far as you can and then wiggle back and forth to enlarge the holes. This will improve aeration to grass roots and also drainage. Brush on some sharp sand - not builders' sand - so it goes into the holes and keeps them open. Poor draiange and compacted soil encourage moss.
In September, apply a Weed and Feed mix - available at DIYs and garden centres but do read the instructions about dosage and weather conditions or you may regret it. If that ends up leaving you with little or no grass left, rake away all the resulting debris and thatch then rake the surface to loosen it and sow fresh grass seed in September. Leave to germinate and grow a couple of inches before its first cut and then mow it on the highest blade setting. Longer grass makes stronger roots for getting thru winter.
Alternatively, just dig the whole thing over completely removing all roots as you go then rake level, firm by trampling with your boot heels, rake again and sow fresh seed or lay turves in September. Plenty of info on making lawns on the RHS website.